Elvin Gadd (過去のオヤ・マー博士 Kakono Oya Mā-hakase[1]) is the younger version of Professor Elvin Gadd who appears in Mario & Luigi: Partners in Time, identical in appearance to his older self, with the exception of his hair being black, his voice being higher pitched and having no wrinkles on his face. Elvin Gadd is encountered in his lab on Thwomp Volcano as it is erupting, studying Thwomps and the history of the volcano itself. During the eruption, Elvin Gadd's lab is destroyed by Thwomps that fall through the building, including a massive, flaming one that is about to explode. Seeing Baby Mario douse the giant Thwomp, the memories of his present-day self suddenly start to be rearranged, and he has the idea of building the Hydrogush 4000.

Afterward, Elvin Gadd mentions that he plans on relocating to an affordable lab at the edge of Boo Woods for "paranormal research", a reference to Luigi's Mansion, and he is not seen again for the rest of the game.